Belt drive for grind mill roll stands



Oct. 20, 1953 K. MGCLELLAND BELT DRIVE FOR GRIND MILL ROLL STANDS 4Sheets-Sheet 1 Filed Feb. 16, 1951 INVENTOR O 1953 K. MQCLELLAND 5 ,815

BELT DRIVE FOR GRIND MILL ROLL STANDS Filed Feb. 16, 1951 4 Sheets-Sheet2 Oct. 20, 1953 K. MQCLELLAND 5,

BELT DRIVE FOR GRIND MILL ROLL STANDS Filed Feb. 16, 1951 4 Sheets-Sheet:5

Oct. 20, 1953 K. M CLELLAND BELT DRIVE FOR GRIND MILL ROLL STANDS 4Sheets-Sheet 4 Filed Feb. 16, 1951 1 N VE NTOR A ORNEY Patented Oct. 20,1953 UNITED STATES PATENT OFFICE BELT DRIVE FOR GRIND MILL ROLL STANDSKenneth McClelland, Chicago, Ill.

Application February 16, 1951, Serial No. 211,275

11 Claims. (Cl. 74-24211) This invention relates to grind mill r011Stands of the type comprising two pairs of belt-driven grinding rolls,each pair of which includes a fast roll and a slow roll, and has aparticular reference to improvements in the arrangement of the rolls andthe belt drive connections between the drive shafts and the grindingrolls of such stands.

In flour mills, the largest users of roll stands of the type disclosedherein, the maintenance of mill balance or the distribution of the millstocks according to the distribution of capacity is essential tosuccessful operation, more important even than uninterrupted twenty-fourhour operation all week long,

Flour milling is a gradual reduction where each roll stand does adefinite type of grinding on a classified stream of stock, the productof that roll stand then passing to certain classification facilities tobe reclassified for further grinding. These classifiers also serve todistribute the mill stock, all of one classification going to itsassigned roll or rolls.

Unbalance in the flour mill reduces both the percentage ofhighest'quality flour and the capacity of the mill as a whole. Highqualit flour erly adjusted for the type and amount of stock flowing toit and running at normal speed, with normal difference in speed of fastand slow rolls.

The variations in mill balance effected by slipping belts on one rollstand are the variations of the product of that roll stand, whichdetermine the loading of subsequent roll stands. As the roll setting ismaintained by stiff spring pressure, appreciable variation of the amountof stock passing through the rolls varies the roll pressure andgranulation of that roll stand, changing the loading of other subsequentroll stands. This unbalanced condition is further complicated by thefact that the classification facilities after'each roll stand arelimited both as to capacity and range of assortment. If any of theseclassifiers are either overloaded or underloaded, they may damage themill stock. Unusual mill stocks fed to a certain classifier Will not besatisfactorily classified.

The control of the milling process is effected by the sampling of theground product beneath each pair of rolls. As both pairs on the samestand are ordinarily set for the same grind, this sampling includescomparison of the product of the two pairs of rolls.

This sampling process is improved if the rolls are symmetrically placed,that is, either the fast roll or the slow roll is placed to the outsideof the roll stand on both sides. The product fans out beneath the pairof rolls, one classification tending to fall beneath the slow roll andanother classification tending to fall beneath the fast roll. Thesampling door is below and outside the outer roll. If the miller reachesin and takes a sample in the same manner on both sides, he gets the samecross section if the rolls are so symmetrically placed. If they areplaced as is now common, one side having the fast roll outside, theother having the slow roll outside, the samples taken in the same manneron the two sides are not alike.

The miller prefers the fast roll outside for facility and safety inreplacing scrapers while running. In grinding with smooth rolls, whichmore than half the roll stands use, scrapers are used to remove the lastof the ground stock from the rolls. The slow roll scraper is notabsolutely essential, if faulty it can be changed at the end of theweek, but the fast roll scraper is required at all times. If the fastroll is outside the replacement of this necessary scraper while runningis much simpler, faster and safer than if the fast rolls are inside theslow roll.

Occasionally a roll stand is choked, despite the power applied, eitherfrom excessive stock wedging in between the rolls, or filling up becausea choke below the stand will not permit the egress of the ground productor the rolls expanding from the heat of rubbing against each otherwithout stock when the flow of stock to the rolls is interrupted.Sometimes the belts will burn off, and occasionally they will kee ondriving and start a fire in the stand. If the belts can be made to flyofi immediately on such overloads and the miller notified by an alarm,the fire hazard, and damage to rolls, bearings and belts will beminimized. The miller cannot always catch these maladjustmentsimmediately because for sixteen of the twenty-four hours there is onlyone man on the grinding floor and he has many duties elsewhere.

Primarily the object of the invention is to provide, between the driveshaft and the fast and slow rolls of a grind mill roll stand of the typementioned, novel belt connections which insure maintenance ofpredetermined speeds of rotation of the fast and slow rolls, and,consequently, constant, uniform grinding actions of the rolls, whereby amaximum amount of high quality flour or other ground product is obtainedfrom any given amount of grain or other material fed between the rolls.

Heretofore, it has been usual in grind mill roll stands of the typementioned to provide, between the drive shaft and the fast rolls, onebelt to drive the fast rolls and, between the drive shaft and the slowrolls, either another belt or a pair of belts and generally acountershaft to control the speed of the slow rolls. In this connection,during grinding, the tendency of the fast rolls is to increase thespeeds of the slow rolls to the speeds of the fast rolls, and, hence, tocause the slow rolls to develop power tending to cause them to over-runtheir speed-retarding drives and to return a certain amount of power.However, according to such usual prior practice the slow roll speedcontrol belt or belts and the countershaft. if used, unnecessarilyduplicates the handling of part of the power, using more belting thannecessary, with attendant loss of efficiency and added maintenance, andneed for attention to the more complex mechanism.

Accordingly, a special object of the present invention is to provide, ina grind mill roll stand of the type mentioned, one belt which connectsthe drive shaft with the fast roll of one pair and the slow roll of theother pair, and another belt which connects the drive shaft with theremaining fast and slow rolls of the two pairs, whereby both belts aread antageously edually loaded and both advantageously operate to utilizethe power developed in the slow rolls while grinding to help drive thefa t rolls without any supplementary belting or mechani m. Otherparticular advantages of the present belt drive arrangement as justoutlined are that belt ten ions are minimized and that, therefore,narrower and less costly belts may be used than heretofore: thatnarrower belts conserve valuable space; and that bearing pressures arereduced with con equent reduction in roll stand maintenance costs.

Another special and important obiect of the invention is to associatewith the belts of the present belt drive arrangement as outlined,simple, practical means of determining and automatically maintainingproper tensions in the belts such that they are effective to tran mitall necessary power for proper operation of any given roll stand undernormal grinding conditions, but are ineffective to tran mit appreciablygreater power, whereby they will ride off their pulleys and topoperation of the roll stand should they for any rea on become overloadedas, for example, due to iamming of material between the rolls of theroll stand. In this way roll damage is minimized and there practicallyis eliminated any possibility of damage to the belts or overheating ofbearings or the occurrence of a fire due to chokes.

Another ob e t of the invention is to provide a roll arrangement similaron the two sides of the roll stand to facilitate ampling of the groundstock, and as far as possible provide for the fast rolls on the outsideto facilitate replacement of the fa t roll scraper.

Another object of the invention is to provide dependab e means fordriving the roll stands with the fiat belts with line haft a shortcenter distance from the rolls to make possible the utilization of theshaft floor for other purposes. The roll floor in a flour mill is abovea shaft floor almost exclusively devoted to the shafting and pulleysnecessary for driving the roll stands.

An additional special and important object of this invention is toprovide a construction and arrangement adaptable to existing roll standsin order to make it useful to industry. Roll stands are long lived;probably 75 of those in the country are over thirty years old; asubstantial percentage are over fifty years old. Very few flour millingcompanies can afford the capital investment required to completelyreplace their r011 stands.

A further object of the invention is to eliminate the tunnel commonlyextending through the roll stand to provide for the countershaftcontrolling the slow rolls. This tunnel bisecting the space for egressof the ground product increases the possibility of choke-up beneath thestand and provides a breeding place for insect infestation.

A still further object of the invention is to provide means whereby asuitable alarm is operated in the event of the development of anabnormal condition in either of the belts of the present belt drive.

With the foregoing and other objects in view, as will become more fullyapparent as the nature of the invention is better understood, the sameconsists in grind mill roll stand arrangement and belt drive connectionssuch as are illustrated by way of example in the accompanying drawingsand as will be hereinafter more fully described and claimed.

In the accompanying drawings, wherein like reference characters denotecorresponding parts in related views:

Figure 1 is a perspective view illustrating more or less schematicallybelt drive connections between the drive shaft and the fast and slowrolls of a ring mill roll stand in accordance with one practicalembodiment of the invention; and

Figures 2, 3 and 4 are views similar to Figure 1 illustrating belt driveconnections in accordance with alternative embodiments of the invention.

Referring to the drawings in detail, it will be observed that, accordingto each of the different illustrated embodiments of the invention, thegrind mill roll stand is of the type comprising two pairs of rolls eachpair of which is composed of a fast roll and a slow roll. The rolls are,of course, disposed horizontally and parallel to each other. Preferably,too, they are disposed in a common horizontal plane, although this isnot essential. In any event, the two pairs are suitably spaced apart andthe rolls of each pair are disposed for grindin cooperation closelyadjacent to each other.

Referring now particularly to the embodiment of the inventionillustrated in Figure l of the drawings, the two fast rolls aredesignated as A, A. and their related slow rolls are designated as B, B.In this connection and as will be noted, each fast roll is disposedoutwardly with respect to its related slow roll. This, however, althougha departure from prior common practice, is preferable but not essential,since the fast rolls may, if desired, be disposed inwardly relative totheir related slow rolls, as will later become apparent.

Each of the rolls A and B includes, as usual, a shaft l0 extended on oneend to accommodate a pulley, said shaft being journaled in a bearing 1 lsuitably mounted upon a frame element I2. whereby the T0115 are mountedfor rotation and in proper relationship to each other. In accordancewith known practice, suitable provision is made whereby one roll of eachpair is adiustable toward and away from its companion roll to vary thefineness of grinding of material fed between the rolls. However, thepresent invention is not concerned with this and therefore it has notbeen illustrated.

Below or otherwise suitably located relative to the rolls A and B is adrive shaft, designated as It, which is horizontally or substantiallyhorizontally disposed and which usually extends parallel orsubstantially parallel to the rolls A and B.

On the shaft ii! of the fast roll A of one pair of the rolls is fixed apulley it which is disposed at one side of the roll stand. On the shaftID of the slow roll B of the other pair of rolls is fixed a companionpulley which is disposed at the same side of the roll stand as thepulley I l and in the same plane as the latter. Similar companionpulleys l6 and I? are fixed to the shafts Iii of the other fast and slowrolls, respectively, at the other side of the roll stand.

On the drive shaft it are fixed two pulleys I8 and 9 the former of whichis disposed for proper alinement with the pulleys I l and i5 and thelatter of which is disposed for proper alinement with the pulleys it andI1.

Engaged with the pulleys l4, l5 and i8 is an endless belt 2!], whichextends directly across the pulleys l4 and It, and directly from theouter sides of the latter to the pulley it, while engaged with thepulley it, It and I9 is an endless belt 2! which likewise extendsdirectly across the pulleys it and II and directly from the outer sidesof the latter to the pulley it. Thus, the fast roll of one pair and theslow roll of the other pair are connected to the drive shaft it by thebelt 23 at one side of the roll stand, and the other fast and slow rollsare connected to the drive shaft I? by the belt 2! at the other side ofthe roll stand.

Preferably the two drive shaft pulleys It and 19 are of equal diameters;preferably the two fast roll pulleys it and it are of equal diameters;and preferably the two slow roll pulleys I5 and l! are of equaldiameters. If so, the slow roll pulleys I5 and i; will, of. course, beof suitably greater diameters than the fast roll pulleys Id and i6,whereby the fast rolls are driven by the shaft It at suitably greaterspeed than the slow rolls. However, corresponding pulleys of the twosets need not be of equal diameters since desired higher speeds of thefast rolls than the slow rolls may be obtained by otherwise suitablyvarying the diameters of the respective pulleys. In any event, one ofthe belts, the belt 20 in the present instance, is crossed so that therolls of each pair are driven inwardly and downwardly relative to eachother.

Suitably cooperating with the belts 2t and 2! is, or are, suitable meansfor automatically maintaining them under constant, predeterminedtensions sufficient to prevent them from slipping relative to theirrelated pulleys under normal load conditions of the roll stand, butinsufficient to prevent either of the same from readily slipping oi'fits related pulleys in the event of minor overloading of either pair ofrolls.

In the drawings, the belt tensioning means referred to is in the form ofa pair of slack take-up pulleys in the event of minor overloading ofeither pair of rolls. The pulleys 22'*-22 are, of course, engaged withthe slack strands of the belts 29 and 2! and may be loaded either byweights 23 or, alternatively, by springs. In either case, their properloading may be determined by varying the values of the weights 23 or thestrengths of the springs, as the case may be during a trial period ofgrinding operation of the roll stand. Thereafter their loading isconstant and is such as to maintain the belts under constant tensions asdescribed under wide range of variation of belt lengths. Alternatively,the drive shaft l3 may be mounted for movement toward and away from therolls A and B and a weight or weight or a spring or springs may beemployed to tend constantly to shift said shaft away from said rolls tomaintain the belts 2i) and 2| under constant tensions as aforesaid.

As will be apparent from the foregoing, not only are the belts 2t and 2imaintained under constant tensions such as to insure predeterminedspeeds of the fast and slow rolls and uniform grinding actions of saidrolls with the output of a maximum amount of high quality groundmaterial under normal load conditions of the roll stand, but theirloading always is of a minimum value not appreciably in excess of thatrequired to adapt them properly to perform their functions. Hence theymay be of minimum widths with the advantages of low cost andconservation of space at either side of the roll stand. In addition,they impose minimum pressures upon the bearings l l and, hence,contribute materially to minimizing maintenance and power costs of theroll stand.

The embodiment of the invention illustrated in Figure 1 of the drawingsmay be used in any instance where the belts 28 and ii are of lengthssuch that they will operate satisfactorily when one of them is crossed,and it has the advantage that the slack sides of the belts do not becometaut at the instant of startirr of operation of the roll stand as wellas the further advantage that the belts exert inward pressures upon thefast roll pulleys with consequent relief of normal grinding pressure onthe fast roll bearings ll.

When the roll mill is in operation the fast rolls act through thematerial being ground to tend to rotate the slow rolls at the samespeeds as the fast rolls. Hence, the drive shaft is not required tofurnish power directly to the slow rolls to drive them. On the contrary,the slow roll, being driven by the fast roll of its pair, acts throughits belt to help drive the fast roll of the other pair. Therefore, themaximum load on each belt is that required to drive its fast roll andthe power drawn from the lineshaft the difference between that requiredby the fast roll and that furnished by the slow roll of the other pair.As this salvage of slow roll power is simple and direct there is minimumloss of power.

Suitable means are provided whereby an alarm is operated in the event ofthe development of an abnormal condition in either of the belts 28 or 2i An abnormal condition of either belt may result from an amount ofstretch thereof such that its slacl; take-up means has reached the endof its effective range of movement, or from the belt having ridden offits pulleys. in either case, one or the other of the idler pulleys 22will move to its limit of movement under the influence of its Weight 23,or equivalently, its spring, or the drive shaft it will move to itslimit of movement under the influence of its weight or weights or pringor sprin as the casemav be. Ther for such movement of either of theidler pulleys or of said drive shaft, may appropriately be employed forthe purpose of operating an alarm. In this connection and as illustratedin the drawings, the pivoted arms 2t upon which the idler pulleys 22 aremounted may each have suitably mounted thereon an electric switch 25 ofa type which maintains the circuit of an electric alarm 26 open as longas the arm and the switch are not tilted beyond a predetermined angle,but which serves to close said circuit upon tilting of said arm and saidswitch beyond said angle. As long as the belts 2i] and 2| are in normalconditions the angles of the arms 23 and of the switches 25 are suchthat said switches are open. When, however, an abnormal condition ofeither belt develops, the related arm 2 and switch 25 assume angularpositions such that the switch closes the alarm circuit. Accordingly,the alarm is operated when an abnormal condition of either beltdevelops.

In some instances the drive shaft [3 may be desired so near the grindrolls as to preclude the possibility of using a crossed belt as in theFigure 1 embodiment of the invention. In any such instance most of thevarious advantages of the belt drive arrangement illustrated in Figure 1of the drawings may be attained by a belt drive arrangement asillustrated in Figure 2 of the drawings.

In Figure 2 of the drawings the arrangements of the grind rolls andtheir pulleys and the drive shaft and its pulleys are the same as in theFigure l embodiment of the invention, except that the drive shaft isdisposed so near the grind rolls that it is impracticable to use one ofthe belts crossed as in the Figure l arrangement. Accordingly, the samereference characters as are employed in Figure 1 are employed in Figure2, with the exponent 2, to designate parts corresponding to parts shownin Figure 1. In other Words, in Figure 2, the fast rolls are designatedas A the slow rolls as B the roll shafts as IE the fast and the slowroll pulleys cf the two sets as M I I5 and H respectively, the driveshaft as l3 its pulleys as I3 I9 and the belts as 29 and 2 i At one sideof the roll stand of the Figure 2 embodiment of the invention one of thebelts has the same arrangement relative to its pulleys as thecorresponding belt of the Figure 1 embodiment of the invention. In otherwords, the belt ZI of Figure 2 has the same arrangement relative to itspulleys :6 I1 and 59 as the corre sponding belt 2! of Figure 1 hasrelative to its pulleys IS, IT and 19. The other belt, 29 of the Figure2 embodiment of the invention, instead of being crossed as in the caseof the corresponding belt 20 of the Figure 1 form of the invention, andinstead of extending directly across the pulleys I4 and !5 as in thecase of the belt 23 with respect to the pulleys l4 and I5, extends fromthe drive shaft pulley A8 to the inner sides of the pulleys I4 and I5outwardly and downwardly over the latter pulleys past said drive shaftpulley I8 and to and about an idler pulley 22 located at the side of thedrive shaft l3 remote from the rolls A and B Thus, the belt 29 connectsthe fast roll of one pair and the slow roll of the other pair to thelineshaft, the belt 2| connects the remaining fast and slow rolls, andthe rolls of each pair are properly driven downwardly and inwardlyrelative to each other.

The belt 20 has the appearance of the slow roll belt used in the commonmethod of driving properly drive the fast rolls.

8 a roll stand without a countershaft. In that slow roll belt, however,the strand passing beneath the lineshaft is not the slack strand whichprecludes automatically slack side tension control through the idlerpulley beneath the lineshaft, which is made possible in the presentdrive.

The pulley 22 may be either a slack take-up pulley or simply a fixedidler pulley. If it is a slack take-up pulley, another slack take-uppulley 22 may be provided to cooperate with the slack strand or reach ofthe belt 2| and both of said slack take-up pulleys 22 may be loaded inthe same manner as the slack take-up pulleys 22 of the Figure 1embodiment of the invention to maintain the belts 2 0 and 2! underconstant tensions sufficient to prevent slip of the same relative totheir associated pulleys under normal load conditions of the roll stand,but insufficient to prevent the same from readily slipping off theirassociated pulleys in the event of abnormal load,- ing of the rolls. If,on the other hand, either pulley 22 or 22 is a fixed idler pulley, thedrive shaft I3 may be mounted for adjustment toward and away from therolls A and B and may be weight or spring loaded to urge it away fromsaid rolls to maintain the belts 20 and 2 I under constant tensions asaforesaid. Moreover, alarm operating means may be associated with eitherthe slack take-up pulleys 22 or 22 or the drive shaft I3 as the case maybe, in the same manner as set forth in connection with the alarmoperating means of the Figure 1 embodiment of the invention.

Obviously, the Figure 2 embodiment of the invention has the sameadvantage as the Figure 1 embodiment of the invention respectingmaintenance of predetermined speeds of the fast and the slow rolls;equal loading of the belts; minimum tension in the belts; minimum widthbelts; conservation of space at the sides of the roll stand; relief onoverloads; better sampling of ground stock; ease of replacement of fastroll scrapers etc., but does not have the fast roll bearing pressure onone side so directed as to relieve the grinding pressure.

According to the embodiments of the invention illustrated in Figures 1and 2 the differences in speed between the fast and the slow rolls isminor and therefore the fast roll pulleys may be amply large to permitthe use of belts in the manner shown in said figures. In some instances,however, it may be desirable to have major differences in speed betweenthe fast and the slow rolls. In such instances, the difference in pulleysizes may be of such as not to permit belts to be best used as in theembodiments of the invention illustrated in Figures 1 and 2 because oflack of sufficient wrap of the belts about the fast roll pulleys to Inany such instance, the heretofore described general features andadvantages of the invention may be attained in embodiments of theinvention as illustrated in Figures 3 and 4 of the drawings.

Referring first to Figure 3 of the drawings, it will be observed thatthe arrangement of the two pairs of grind rolls and the drive shaft isgenerally the same as in the Figure 1 embodiment of the invention, butthat the positions of the rolls of each pair are reversed as comparedwith the said Figure 1 roll arrangement. That is to say, the fast rollof each pair is disposed inwardly instead of outwardly with respect toits companion slow roll. However, the same elements are involved in theFigure 3 embodiment of the invention as in the Figure l embodiment ofthe invention. Accordingly, the same reference characters as areemployed in Figure 1 are employed in Figure 3, with the exponent 3 todesignate parts corresponding to parts shown in Figure 1. Thus, inFigure 3, the fast rolls are designated as A the slow rolls as 13 theroll shafts as H3 the roll pulleys as I4 I5 E6 and IF, the drive shaftas I3 its pulleys as I8 and E9 and the belts as and 2| At each side ofthe Figure 3 roll stand the related belt, instead of extending directlyacross the related fast and slow roll pulleys, as in the Figure 1embodiment of the invention, extends downwardly between said fast andslow roll pulleys and beneath idler pulleys 22 and 22 on the slackstrand located nearer the drive shaft I3 than the fast and the slow rollpulleys, whereby ample wrap of each belt about its related fast rollpulley of comparatively small diameter is attained. Otherwise, theFigure 3 embodiment of the invention is the same, in all essentialrespects as the Figure 1 embodiment of the invention. That is to say,one of the Figure 3 belts is crossed to provide for downward and inwardrotation of the rolls of each pair; the belts are tensionecl to theextent of the belts of the Figures 1 and 2 forms of the invention eitherby means of the pulleys 22 or 22 or by means of the drive shaft I3 andalarm operating means either are associated with the pulleys 22* or 22or with the drive shaft I3 as the case may be, in the manner heretoforedescribed.

The Figure 3 embodiment of the invention is suitable for use in anyinstance where fast roll pulleys of small diameters are used and wherethe drive shaft is spaced sufficiently from the grind rolls to permitone of the belts to be crossed. In any instance where fast roll pulleysof small diameters are used and where the drive shaft is disposed soclose to the grind rolls as not to permit one of the belts to becrossed, an arrangement of the belts as illustrated in Figure 4 of thedrawings may be employed. According to Figure 4 the arrangement of thebelts is the same as in Figure 3, except, on the one hand, that neitherof the belts is crossed, and except, on the other hand, that one of thedrive shaft pulleys, instead of being mounted directly on the driveshaft, is mounted on a countershaft 2'l connected by gears 28 to thedrive shaft to insure downward and inward rotation of the rolls of eachpair relative to each other.

Since, except for the countershaft 27 and the gears 28, the Figure 4embodiment of the invention the same in all essential respects as theFigure 3 embodiment of the invention, the same reference characters asare employed in Figure 3 are employed in Figure 4, with the exponent 4,to designate parts corresponding to parts shown in Figure 3.

According to the Figure 4 embodiment of the invention, either therollers 22 or 22 may be loaded to tension the belts 20 and 21 to theextent set forth in connection with the other embodiments of theinvention, or, alternatively, the drive shaft I3 and its associatedcountershaft 27 may be adjustable and may be properly loaded for thispurpose. Likewise, alarm operating means may be associated with eitherthe pulleys 22 or the shafts l3 and 27 in the manner set forth inconnection with the other embodiments of the invention.

Obviously, the Figures 3 and 4 embodiments of the invention have thesame advantages as the Figures 1 and 2 embodiments of the inventionrespecting maintenance of predetermined speeds of the fast and the slowrolls; equal loading of the belts; minimum tension in the belts; minimumbelt widths; conservation of space at the sides of the roll; relief onoverloads; better sampling of ground stock but does not have theadvantage of ease of replacement of fast roll scrapers, or the fast rollbearing pressure directed so as to release the grinding pressure.

As will be understood, of course, all forms of the present inventioncontemplate the use of flat belts in order that the belts may readilyride off their pulleys under overload conditions.

From the foregoing description considered in connection with theaccompanying drawings, it is believed that the construction and'mode ofoperation of a grind mill roll stand having belt drives in accordancewith any of the different embodiments of the present invention will beclearly understood and its advantages appreciated. It is desired topoint out, however, that while only certain specific embodiments of theinvention have been illustrated and described, the same is readilycapable of other specifically different embodiments within its spiritand scope as defined in the appended claims.

I claim:

1. A grind mill roll stand including, two pairs of rolls each paircomprising a fast roll and a slow roll, like rolls symmetrically placedwith respect to the center line of the roll stand; companion rollpulleys one fixed to the fast roll of one pair and one fixed to the slowroll of the other pair at one side of the roll stand, similar companionpulleys fixed to the other fast and slow rolls, respectively, at theother side of the roll stand; a drive shaft having fixed thereto twodriving pulleys one alined with the companion roll pulleys at one sideof the roll stand and the other alined with the companion roll pulleysat the other side of the roll stand, and an endless belt at each side ofthe roll stand each engaged over the pulleys of the fast and the slowrolls and the related drive shaft pulleys at its side of the roll stand,the slack side of each belt leading to its related fast roll, and eachoperable to rotate its related fast and slow rolls in the same directionbut oppositely to the direction in which the other fast and slow rollsare rotated by the other belt.

2. A grind mill roll stand including, two pairs of rolls each paircomprising a fast roll and a slow roll, like rolls symmetrically placedwith respect to the center line of the roll stand; companion rollpulleys one fixed t0 the fast roll of one pair and one fixed to the slowroll of the other pair at one side of the roll stand, similiar companionpulleys fixed to the other fast and slow rolls, respectively, at theother side of the roll stand, a drive shaft having fixed thereto twodriving pulleys one alined with the companion roll pulleys at one sideof the roll stand and the other alined with the companion roll pulleysat the other side of the roll stand, an endless belt at each side of theroll stand each engaged over the pulleys of the fast and the slow rolland the related drive shaft pulleys at its side of the roll stand andeach operable to rotate its related fast and slow rolls in the samedirection but oppositely to the direction in which the other fast andslow rolls are rotated by the other belt, an idler "pulley engaged withthe slack side of each belt, and means maintaining a load on each idlerpulley to automatically maintain each belt under a constantpredetermined slack side tension sufficient to prevent slip of the beltrelative to its 3. A grind mill roll stand as set forth in claim 2 inwhich the fast rolls are disposed outwardly with respect to the slowrolls.

4. A grind mill roll stand as set forth in claim 2 in which each beltextends directly from its related fast roll pulley to its related slowroll pulley.

5. A grind mill roll stand as set forth in claim 2'in which one of thebelts is crossed.

6. A grind mill r'oll stand as set forth in claim 2 in which each of thebelts extends directly from its related fast roll pulley to its relatedslow roll pulley and in which one of the belts is crossed.

7. A grind mill roll stand as set forth in claim 2 in which one of thebelts extends directly from its related fast roll pulley to its relatedslow roll pulley, and in which the other belt extends from the relateddrive shaft pulley to the inner sides of the related fast and slow rollpulleys then over the latter pulleys and then to and about an idlerpulley located at the side of the drive shaft remote from the rolls.

8. A grind mill roll stand as set forth in claim 2 including a pair ofidler pulleys one associated with the companion fast and slow rollpulleys at one side of the roll stand and the other associated with thecompanion fast and slow roll pulleys at the other side of the roll standand each located nearer the drive shaft than the related fast and slowroll pulleys, and in which each belt extends from its related slow rollpulley first about the related idler pulley and then to the related fastroll pulley.

9. A grind mill roll stand as set forth in claim 2 including a pair ofidler pulleys one associated with the companion fast and slow rollpulleys at one side of the roll stand and the other associated with thecompanion fast and slow roll pulleys at the other side of the roll standeach located nearer the drive shaft than the related fast and slow rollpulleys, and in which each belt extends from its related slow rollpulley first about the related idler pulley and then to the related fastroll pulley, and in which one of said belts is crossed.

10. A grind mill roll stand having two pairs of rolls each paircomprising a fast roll and a slow roll, companion roll pulleys one fixedto the fast roll of one pair and on fixed to the slow roll'of the otherpair at one side of the roll stand, similar companion pulleys fixed tothe other fast and slow rolls, respectively, at the other side of theroll stand, a drive shaft having fixed thereto a drive pulley alinedwith the companion pulleys at one side of the roll stand, 'acountershaft geared to said drive shaft for reverse rotation relativethereto, a drive pulley fixed to said countershaft and alined with thecompanion pulleys at the other side of the roll stand, an idler pulleyat each side of the roll stand located nearer the drive' shaft than thecompanion fast and slow roll pulleys, and an endless belt at each sideof the roll stand, each belt extending from its related drive pulley tothe outer sides of the related fast and slow roll pulleys and from thelatter to and about the related idler pulley.

11. A grind mill roll stand having two pairs of rolls each paircomprising a fast roll on the inside and a slow roll on the outside,companion roll pulleys one fixed to the fast roll of one pair and onefixed to the slow roll of the other pair at one side of the roll stand,similar companion pulleys fixed to the other fast and slow rolls,respectively, at the other side of the roll stand, a drive shaft havingfixed thereto a drive ulley alined with the companion pulleys at oneside of the roll stand, a countershaft geared to said drive shaft forreverse rotation relative thereto, a drive pulley fixed to saidcountershaft and alined with the companion pulleys at the other side ofthe roll stand, an idler pulley at each side of the roll stand locatednearer the drive shaft than the companion fast and slow roll pulleys, anendless belt at each side of the roll stand, each belt ex- 7 tendingfrom its related drive pulley to the outer sides of the related fast andslow roll pulleys and from the latter to and about the related idlerpulley, and means automatically maintaining each belt under a constantpredetermined tension sufficient to prevent slip of the same relative toits related pulleys under normal load conditions of the roll stand, butinsufficient to prevent the belt from readily slipping off its pulleysin the event of only minor abnormal loading of the roll stand.

KENNETH MCCLELLAND.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 178,063 King -1 May 30, 1876 250,954 Odell Dec. 13, 1881252,945 Holt Jan. 31, 1882 260,225- Odell June 27, 1882 298,206 Holt May6, 1684 333,866 Lauholf Jan. 5,1886 334,460 Obenchain Jan. 19, 1886382,583 Barnard May 8, 1888 385,420 Mawhood July 3', 1888 1,949,119Gibbs Feb. 27, 1934 2,418,464 Corwin Apr. 8, 1947 FOREIGN PATENTS NumberCountry Date 11,641 Great Britain 1885 4,011 Great Britain Dec. 18, 189732,758 Germany Aug. 31, 1885

